1. Field of the Invention
The present invention relates to a light emitting diode (LED) having uniform wavelength conversion characteristics, a manufacturing method of the LED, an LED module, and a manufacturing method of the LED module.
2. Description of the Related Art
A light emitting diode (LED) chip is a semiconductor device that converts electrical energy to optical energy. The LED chip includes a compound semiconductor generating light having a particular wavelength according to an energy band gap. Use of LEDs is expanding to a field of displays such as a mobile display and a computer monitor, a field of a back light unit (BLU) for a liquid crystal display (LCD), and even a field of lighting.
Generally, an LED is manufactured by applying a phosphor resin to an upper portion of an LED chip so that the LED may generate light having a desired wavelength. For example, a white LED having a convex hemispherical surface may be manufactured by dispensing the phosphor resin onto the upper portion of the LED chip.
According to another example, a mask may be placed on a substrate to expose at least one LED chip mounted on the substrate, and phosphor resin may be printed. Next, the mask may be removed, thereby manufacturing a white LED having a rectangular parallelepiped surface.
However, in the foregoing conventional methods, uniform white light may not be obtained since the phosphor resin is applied non-uniformly. When uniformity of the phosphor resin is extremely low, non-uniformity of color distribution may be so increased that the LED may be inapplicable to products. As a result, yield may be affected.
When the phosphor resin is applied by dispensing, the process is performed chip by chip. Therefore, productivity per unit time is considerably reduced. Furthermore, when printing of the phosphor resin is performed using the mask, the phosphor resin may be deformed as the mask is removed.
A structure that modularizes the LED package by mounting the LED package on a printed circuit board (PCB) may have a limit to miniaturization of an LED module, and may not decrease a price of the LED module due to a high error rate during at least two mounting processes. A luminance and a color of the LED package may have a deviation due to a deviation in a wavelength and a luminance of an LED, a manufacturing tolerance associated with handicrafts, such as a lead frame and the like, and a process tolerance associated with a phosphor coating process, a lens molding process, and the like.
To improve an optical uniformity of the LED module, such as the luminance and a color uniformity of the LED module as a resultant product, various LEDs having different luminance degrees and colors may be grouped by performing binning, and LEDs in different groups may be used together.
A phosphor layer forming method for forming a phosphor layer in the LED may coat a substrate with a phosphor before mounting of an LED chip on the substrate so that a white light is emitted at an LED chip level. Examples of such a method include an electrophoresis scheme, a spray scheme, a printing scheme, a molding scheme, a phosphor pre-form attaching scheme, and the like.
In a case of a vertical LED chip, a method of forming a phosphor layer on a chip that is already attached to a substrate may include attaching, using a conductive adhesive, an LED chip on the substrate including wiring, connecting an electrode with another electrode by wire bonding, coating a top side with a transparent adhesive, and attaching a phosphor pre-form to the top side. However, the foregoing method has a difficulty in manufacturing the LED chip providing a white light and has a limit to decrease of color dispersion in an LED package level.
A range of the color dispersion demanded by the market is decreasing and a decrease in the color dispersion may determine the competitiveness that is directly associated with a quality and a yield. Therefore, there is a desire for a method of obtaining a high yield to decrease the range of the color dispersion and to improve productivity and competitiveness.